Memory Information Transfer Power Management

ABSTRACT

An apparatus and method for conserving power in a memory information transfer system. The system may include a direct memory access (DMA) controller coupled to a memory storage device and a peripheral device. The DMA controller transfers information from the memory storage device to a buffer in the peripheral device. The DMA controller may also transfer information from the buffer in the peripheral device to the memory storage device. When the peripheral device buffer does not have to be filled or emptied by the DMA controller, the DMA controller enters a standby mode. When the peripheral device buffer is full or empty, the DMA controller exits standby mode, empties or fills the peripheral device buffer, and reenters standby mode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to the following co-pending applications:

-   U.S. patent application Ser. No. ______, entitled “STANDBY MODE FOR    POWER MANAGEMENT” filed ______, 2005;-   U.S. patent application Ser. No. ______, entitled “IDLE MODE FOR    POWER MANAGEMENT” filed ______, 2005; and-   U.S. patent application Ser. No. ______, entitled “DISPLAY POWER    MANAGEMENT” filed ______, 2005.

FIELD OF THE INVENTION

The present invention generally relates to power management duringinformation transfer in a memory system. More particularly, theinvention relates to power management in a direct memory access (DMA)system. Still more particularly, the invention relates to powermanagement in a DMA system through the control of power and clocksignals.

BACKGROUND OF THE INVENTION

Direct memory access (DMA) uses a DMA controller to transfer informationbetween components in an electronic device. In a device without DMAcapability, a processor may transfer information between components. Byimplementing a DMA system, the task of transferring information betweencomponents of the electronic device shifts from the processor to the DMAcontroller, thus allowing the processor to perform other tasks, such asexecuting instructions or performing calculations.

The DMA controller may transfer information between peripheral devicecomponents that are external or internal to the electronic device. Forexample, peripheral devices may include memory devices such as hard diskdrives, compact disk (CD) drives, digital video disk (DVD) drives,memory cards, and other devices capable of storing information.Peripheral devices may further include universal asynchronousreceiver/transmitters (UARTs), audio interfaces, universal serial bus(USB) interfaces, and other devices capable of processing, transferring,or storing information.

A peripheral device normally includes a buffer, which is a memorystorage device used to temporarily store information. The DMA controllerfills the peripheral device's buffer with information from theelectronic device's main memory or another peripheral device. Theperipheral device then processes, stores, or transmits the informationin the buffer, eventually sending a request to the DMA controller whenmore information is needed to fill the buffer. The DMA controller mayalso transfer information from the peripheral device's buffer to theelectronic device's main memory or another peripheral device.

If the peripheral device takes an amount of time to process, store, ortransmit the information, the DMA controller has to wait the amount oftime before filling the peripheral device's buffer with more informationor retrieving information from the buffer. While the DMA controllerwaits to fill or empty the peripheral device buffer, an active power andclock signal are transmitted to the idle DMA controller. A communicationbus may transfer information between the DMA controller and theperipheral device. An active power and clock signal may also betransmitted to the communication bus while the DMA controller is idle.Thus, the DMA controller and the communication bus may consume powereven when the DMA controller and the communication bus are notinteracting with the peripheral device.

DMA systems are present in electronic devices such as portablecomputers, portable music players, cellular telephones, personal digitalassistants (PDAs), portable gaming devices, and other devices dependenton battery power. Reducing the consumption of power allows batterypowered portable electronic devices to operate for longer periodswithout recharging the batteries. Thus, it would be beneficial to reducepower consumption by making the DMA controller inactive when thecontroller is not interacting with a peripheral device. It would also bebeneficial to reduce power consumption by other components of the DMAsystem that are idle when no DMA transfer occurs.

SUMMARY OF THE INVENTION

The problems noted above are solved by an apparatus comprising a controlmodule, a memory access device coupled to the control module, aninformation source coupled to the memory access device, and aninformation destination coupled to the memory access device. The memoryaccess device, which may be a DMA controller, is capable of entering apower saving state. The DMA controller enters the power saving state ifall DMA channels are disabled, no new DMA requests are received, and theDMA controller does not need to perform a read request or a writerequest.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, in accordance with some embodiments of the invention, shows apower and clock control module (PCCM) coupled to an initiator module,interconnect module, and target module;

FIG. 2, in accordance with some embodiments of the invention, shows aPCCM coupled to initiator modules, an interconnect module, and targetmodules;

FIG. 3 shows a state diagram with the states for standby mode in a DMAcontroller in accordance with some embodiments of the invention; and

FIG. 4 shows a state diagram of the system shown in FIG. 2 in accordancewith some embodiments of the invention.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components and configurations. As oneskilled in the art will appreciate, companies may refer to a componentby different names. This document does not intend to distinguish betweencomponents that differ in name but not function. In the followingdiscussion and in the claims, the terms “including” and “comprising” areused in an open-ended fashion, and thus should be interpreted to mean“including, but not limited to . . . ” Also, the term “couple” or“couples” is intended to mean either an indirect or direct electricalconnection. Thus, if a first device couples to a second device, thatconnection may be through a direct electrical connection or though anindirect electrical connection via other devices and connections.Furthermore, the term “information” is intended to refer to any data,instructions, or control sequences that may be communicated betweencomponents of the device. For example, if information is sent betweentwo components, data, instructions, control sequences, or anycombination thereof may be sent between the two components.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In accordance with some embodiments of the invention, in an electronicdevice, a DMA controller couples to a peripheral device and a memorystorage device. The DMA controller may transfer information between theperipheral device and the memory storage device through a DMA channeland an interconnect module. The DMA controller may enter standby modewhen the DMA controller no longer interacts with the peripheral deviceor the memory storage device. Thus, the DMA controller may enter standbymode when no DMA channels are active, no DMA requests have been sent,and there is no information to be transferred by the DMA controller.Power and a clock signal may be limited or removed from the DMAcontroller in standby mode, thereby reducing power consumption in theelectronic device.

The standby mode is described in detail in the copending, commonlyassigned patent application “Standby Mode for Power Management” byDahan, et al., Ser. No. ______, filed ______. Additionally, idle modereferenced below is described in detail in the copending, commonlyassigned patent application “Idle Mode for Power Management” by Dahan,et al., Ser. No. ______, filed ______.

Referring to FIG. 1, a power and clock control module (PCCM) 100 couplesto an initiator module 120, interconnect module 130, and target module140. PCCM 100 provides power and a clock signal to each module throughpower line 111 and clock line 112. Power line 111 provides power tologic circuits in each module, and clock line 112 provides a clocksignal to logic circuits in each module for control and synchronization.In some embodiments of the invention, clock line 112 may provideidentical clock signals to each module, derived clock signals to eachmodule, independent clock signals to each module, or multiple clocksignals to each module from PCCM 100. In some embodiments of theinvention, PCCM 100 may be capable of selectively turning on and offpower and clock signals to initiator module 120, interconnect module130, and target module 140.

In the electronic device shown in FIG. 1, interconnect module 130couples to both initiator module 120 and target module 140. Interconnectmodule 130 may be any logic circuitry capable of routing information,such as data, instructions, and control sequences, from initiator module120 to target module 140. Further, interconnect module 130 maycommunicate interrupts and DMA requests between target module 140 andinitiator module 120. An interrupt is a signal that momentarilyinterrupts initiator module 120 processing and indicates to initiatormodule 120 that a predefined event has occurred within target module140. The initiator module 120 may be a DMA controller, and a DMA requestmay be a request from the target module 140 to the DMA controller thatis initiator module 120 to transfer information to the target module.

Interconnect module 130 may be a bus, which may be described as a set ofconductors for communication between initiator modules and targetmodules of the electronic device. Interconnect module 130 may be aninterconnection network, which is a collection of buses connectedtogether to form a mesh with nodes at the bus intersections, the busesincluding logic circuitry that can route information from one module toanother module. Further, interconnect module 130 may be any other devicecapable of routing information between modules.

Initiator module 120 is any logic circuitry within an electronic devicethat generates write or read requests. Initiator module 120 may be aprocessor, direct memory access (DMA) controller, digital signalprocessor (DSP), video accelerator, peripheral device, or any other typeof device capable of initiating write or read requests. Initiator module120 connects to interconnect module 130 through connection 125.

Target module 140 is any logic circuitry that is the destination of awrite or read request. Target module 140 may be a memory device, such asa register, cache, external or internal static random access memory(SRAM) or dynamic random access memory (DRAM), or a peripheral device,such as a display device or an external hard drive. Interconnect module130 connects to target module 140 through connection 141.

Initiator module 120, for example, may be a DMA controller capable oftransferring information from a memory device (not shown in FIG. 1) totarget module 140, which may be a peripheral device, such as an externalhard drive. When initiator module 120 generates a write request to theexternal hard drive that is target module 140, interconnect module 130coordinates the request to the external hard drive. In some embodimentsof the invention, multiple initiator modules 120 and target modules 140may be present and interconnect module 130 may serve to coordinate theflow of information between the modules.

Modules in an electronic device may include circuitry which are notcontiguously placed next to each other but rather distributed throughoutthe device. Thus, the initiator module 120, interconnect module 130, andtarget module 140 shown in FIG. 1 may be considered a logicalpartitioning of the circuits on an electronic device rather than aphysical partitioning. For example, consider a chip containing thecircuitry for a processor and a cache. The processor circuitry may belocated on different parts of the chip and contiguous to or mixed inwith the cache circuitry. Circuitry for the processor may be logicallygrouped into an initiator module and the circuitry for the cache may belogically grouped into a target module. Similarly, the chip may containbus circuitry that is distributed along different parts of the chip andwhich connects the processor circuitry and cache circuitry. The buscircuitry may be logically grouped into an interconnect module.

When initiator module 120 no longer initiates read or write requests totarget module 140, PCCM 100 may deactivate or limit power and the clocksignal transmitted to initiator module 120 to reduce power consumed bylogic circuitry in initiator module 120. Thus, initiator module 120 mayenter a standby mode in which it consumes less power and may not use theclock signal. Initiator module 120 may exit standby mode if a read orwrite request needs to be initiated to other components of the device.To exit standby mode, initiator module 120 informs PCCM 100 to activatethe power and the clock signal.

In some embodiments of the invention, as described above, initiatormodule 120 may detect when it may be able to enter standby mode.Initiator module 120 communicates to PCCM 100 that initiator module 120is ready to enter standby mode under conditions as described below. Forinstance, initiator module 120 may detect that no read or write requestshave been initiated over a number of clock cycles. Initiator module 120may then communicate to PCCM 100 by activating a standby signal througha standby line 150 as shown in FIG. 1. Once initiator module 120activates the standby signal, initiator module 120 may no longerinitiate requests to target module 140. Initiator module 120 entersstandby mode after PCCM 100 activates the wait signal to initiatormodule 120 through wait line 150.

When initiator module 120 enters standby mode, PCCM 100 may reduce oreliminate power sent to initiator module 120 and turn off the clocksignal transmitted to initiator module 120. Alternatively, PCCM 100 mayreduce the frequency of the clock signal. Thus, initiator module 120 mayutilize the clock signal while reducing power consumption. Power andclock signals to interconnect module 130 and target module 140 may alsobe removed. In some embodiments of the invention, PCCM 100 may reduce oreliminate power to initiator module 120 and turn off the clock signal toinitiator module 140 once initiator module 120 enters standby mode andother modules capable of generating DMA requests are idle.

If an event wakes up initiator module 120 from standby mode, initiatormodule 120 deactivates the standby signal. However, PCCM 100 may notdeactivate the wait signal until the power and clock signals toinitiator module 120, interconnect module 130, and target module 140from PCCM 100 reach steady state operating conditions. Only after theclock and power signals have reached steady state and PCCM 100 hasdeactivated the wait signal does initiator module 120 exit standby modeand resume normal operation. In some embodiments of the invention,initiator module 120 may not execute instructions or initiate requeststo target module 140 until PCCM 100 deactivates the wait signal. In someother embodiments of the invention, initiator module 120 may be designedto operate in a low power or low clock frequency environment duringstandby mode to perform “background” processing.

When initiator module 120 enters standby mode, PCCM 100 may deactivateor limit the power and the clock signal transmitted to target module 140to reduce the power consumed by the logic circuitry in target module140. Thus, the target module may enter an idle mode in which it consumesless power and may not use one or more clock signals from PCCM 100. Ifmultiple initiator modules connect to PCCM 100 and interconnect module130, PCCM 100 may deactivate or limit the power and the clock signal totarget module 140 if all initiator modules are in standby mode that arecapable of sending requests to target module 120. Target module 140 mayexit idle mode if initiator module 120 exits standby mode or targetmodule 140 needs to interrupt or communicate with initiator module 120.

For target module 140 to enter idle mode, PCCM 100 first activates anIdleReq signal to target module 140 through an IdleReq line 121 wheninitiator module 120 enters standby mode. If the IdleReq signal isactive and target module 140 does not need to transmit an interrupt orcommunicate with initiator module 120, an IdleAck signal is activated toPCCM 100 through an IdleAck line 122. Once the IdleAck signal isactivated, target module 140 may be in idle mode and may no longertransmit interrupt signals or communicate with initiator module 120.When PCCM 100 receives the IdleAck signal, PCCM 100 may reduce oreliminate power sent to target module 140 and turn off one or more clocksignals transmitted to target module 140, depending on the level oftarget module 140 functionality in idle mode. Alternatively, PCCM 100may reduce the frequency of the one or more clock signals to targetmodule 140. Thus, target module 140 may utilize the one or more clocksignals while reducing power consumption.

Target module 140 may not communicate with any modules in the deviceother than PCCM 100 while in idle mode. If target module 140 needs tocommunicate with other components of the device, target module 140 mustexit idle mode before any communication may occur. If a condition whichmay cause target module 140 to wakeup from idle mode occurs, asdescribed below, target module 140 may activate a wakeup signal to PCCM100 through a wakeup line 123. After PCCM 100 receives the wakeupsignal, PCCM 100 returns the power and clock signals to steady stateoperating conditions. PCCM 100 then deactivates the IdleReq signal, andtarget module 140 deactivates the IdleAck signal and exits idle mode.

Target module 140 may also wakeup from idle mode if initiator module 120exits standby mode. Thus, PCCM 100 returns the power and clock signalsto steady state operating conditions and deactivates the IdleReq signal.Target module 140 may then receive and process requests from initiatormodule 120.

If all initiator modules and target modules connected to theinterconnect module 130 are in standby mode or idle mode, respectively,the interconnect module 130 may enter a power saving mode because theinterconnect module 130 may not have information to transmit. In powersaving mode, PCCM 100 may deactivate or limit power and the clock signaltransmitted to the interconnect module 130. PCCM 100 may activate powerand the clock signal to interconnect module 130 if an initiator module120 or target module 140 exits standby mode or idle mode, respectively.

This technique of placing initiator module 120 in standby mode, targetmodule 140 in idle mode, and interconnect module 130 in power savingmode may reduce power consumption within the electronic device. Forexample, while the amount of power saved each time a target module 140enters idle mode may not be significant, the cumulative effect of powersaved over time with target module 140 in idle mode may be considerable.Because multiple initiator modules 120, interconnect modules 130, andtarget modules 140 may be present in the device, standby mode in theinitiator module, idle mode in the target module and power saving modein the interconnect module may save significant amounts of power. Thus,standby mode, idle mode, and power saving mode allow battery powereddevices, such as laptop computers, portable music players, cellulartelephones, personal digital assistants (PDA), and other portableelectronic devices, to reduce power consumption and increase batterylife.

As described above, a direct memory access (DMA) controller may transferinformation between components in an electronic device. A DMA controllermay be an initiator module because it initiates read and write requeststo components in the electronic device. As shown in FIG. 2, initiatormodules 215 may be a DMA controller 200, digital signal processor (DSP)205, and microcontroller unit (MCU) 210. The initiator modules 215connect to interconnect module 130 through bus 220. Interconnect module130 also connects to target modules 225 through bus 230. The targetmodules 225 may be an audio interface 235, peripheral device 240, andmemory storage device 245.

PCCM 100 couples to the initiator modules 215, interconnect module 130,and target modules 225. PCCM 100 connects to each initiator modulethrough a power line, a clock line, a wait line, and a standby line.These lines connecting PCCM 100 to each initiator module are not shownin FIG. 2 but resemble power line 111, clock line 112, wait line 151,and standby line 150 shown in FIG. 1. The power line, clock line, waitline, and standby line connecting PCCM 100 to the initiator modules 215are represented by bus 250. As described above, each initiator module iscapable of entering standby mode.

PCCM 100 couples to each target module through a power line, clock line,IdleReq line, IdleAck line, and wakeup line. These lines connecting PCCM100 to each target module are not shown in FIG. 2 but resemble the powerline 111, clock line 112, IdleReq line 121, IdleAck 122, and wakeup line123 shown in FIG. 1. The power line, clock line, IdleReq line, IdleAckline, and wakeup line connecting PCCM 100 to the target modules 225 arerepresented by bus 255. As described above, each target module iscapable of entering idle mode.

PCCM 100 also connects to interconnect module 130 through a power lineand a clock line. The power line and clock line are represented by bus260. Power and the clock signal may be removed from interconnect module130 if the initiator modules 215 and target modules 225 shown in FIG. 2enter standby mode or idle mode, respectively, and no longer transferinformation through interconnect module 130. Bus 260 may also include anIdleReq line and an IdleAck line connecting interconnect module 130 andPCCM 100. Thus, interconnect module 130 may be capable of entering idlemode.

In some embodiments of the invention, a large amount of audio data maybe stored in memory storage device 245. The audio data may be sent toaudio interface 235 as described below to be further transferred to aspeaker 265 through connection 270. Audio interface 235 contains anaudio interface buffer 290. Audio interface 235 transfers audioinformation stored in audio interface buffer 290 to speaker 265. In someembodiments of the invention, audio circuitry (not shown in FIG. 2)capable of manipulating audio information may couple between audiointerface 235 and speaker 265. In some other embodiments of theinvention, audio interface 235 may connect to a microphone (not shown)and may transfer audio information from the microphone to memory storagedevice 245 using DMA controller 200.

When transferring audio information from memory storage device 245 toaudio interface 235, microcontroller unit 210 instructs DMA controller200 to transfer the audio information to the audio interface 235. DMAcontroller 200 then reads information from memory storage device 245,stores the information in a DMA buffer 280, and writes the informationto audio interface buffer 290. DMA controller 200 transfers informationto audio interface 235 through a DMA channel (not shown) throughinterconnect module 130. Thus, the DMA channel is an information pathfrom DMA controller 200 to audio interface 235 or another target module.Multiple DMA channels may be present in the system shown in FIG. 2. Insome embodiments of the invention, DMA channels may be directlyconnected between DMA controller 200 and target modules 225. In someother embodiments of the invention, DMA channels may connect to targetmodules 225 through interconnect module 130.

The audio information to be transferred to audio interface 235 may belarger than the storage capacity of audio interface buffer 290.Therefore, DMA controller 200 fills audio interface buffer 290 withaudio information from memory storage device 245. Audio interface 235then transfers the audio information to speaker 265. When audiointerface buffer 290 needs more audio information, audio interface 235sends a communication to DMA controller 200. When DMA controller 200receives the communication, DMA controller 200 may transfer more audioinformation to audio interface buffer 290.

The output rate of DMA controller 200 is usually much higher than theoutput rate of the audio interface. This is because audio interface 235may take a long period of time to transfer audio information from audiointerface buffer 290 to speaker 265. During this time, DMA controller200 may be waiting to fill audio interface buffer 290. In order toconserve power, DMA controller 200 may enter standby mode when it is notactive. PCCM 100 may reduce or eliminate power to DMA controller 200 andturn off the clock signal transmitted to logic circuitry in DMAcontroller 200.

To request entry into standby mode, DMA controller 200 may activate thestandby signal. When the standby signal is active, DMA controller 200may detect a wakeup event, such as a DMA request from themicrocontroller unit or communication from a target module, and respondafter deactivating the standby signal. After PCCM 100 activates the waitsignal to DMA controller 200, PCCM 100 enters idle target modules 225into idle mode. PCCM 100 may remove power and the clock signal to someor all of the logic circuitry in DMA controller 200, placing the DMAcontroller 200 into standby mode. Interconnect module 130 and targetmodules 225 power consumption may be reduced similarly. DMA controller200 may exit standby mode if it detects a DMA request or othercommunication. For example, microcontroller 210 may instruct DMAcontroller 200 to transfer information or communication from the audiointerface may be received, thus waking DMA controller 200 from standbymode.

When audio interface buffer 290 is almost empty, audio interface 235 maysend a wakeup event to PCCM 100 to resume power and the clock signal toaudio interface 235 and interconnect module 130. Audio interface 235exits idle mode and may send a communication to DMA controller 200through interconnect module 130. As described above, DMA controller 200may exit standby mode and fill audio interface buffer 290. Once DMAcontroller 200 fills audio interface buffer 290 and no longer initiatesread or write requests, DMA controller 200 may return to standby mode.This process continues until all the audio information is transferredfrom memory storage device 245 to audio interface 235.

Turning now to FIG. 3, a state diagram describing standby mode in DMAcontroller 200 includes the following states: normal operating state300, ready for standby mode state 320, delaying communication state 335,standby mode state 360, and waiting state 371. In normal operating state300, DMA controller 200 is active 305 and may initiate write or readrequests to target modules 225. When no DMA requests or othercommunications have been received and DMA controller 200 has no activeDMA channels and no longer initiates write or read requests 310, DMAcontroller 200 may enter ready for standby mode state 320.

In ready for standby mode state 320, DMA controller 200 activates thestandby signal to PCCM 325. Once the standby signal has been activated,DMA controller 200 may no longer communicate with target modules 225. IfDMA controller 200 needs to initiate write or read requests 330 totarget modules 225, DMA controller 200 may enter a delayingcommunication state 335 and deactivate the standby signal 340. In readyfor standby mode state 320, for instance, DMA controller 200 may receivea communication from audio interface 235, thus indicating that the DMAcontroller 200 should wake up, exit standby mode, and transferinformation to audio interface 235. DMA controller 200 may transition todelaying communication state 335 if microcontroller 210 instructs DMAcontroller 200 to transfer information. DMA controller 200 thendeactivates the standby signal 340. Furthermore, in delayingcommunication state 335, DMA controller 200 may perform processingrelated to the received DMA request from microcontroller unit 210 orcommunication with audio interface 235. However, DMA controller 200 maynot communicate with other modules in the device other than PCCM 100 fora variable amount of time in accordance with the embodiments of the DMAcontroller. Once the delay time 345 passes and the wait signal is notasserted, DMA controller 200 may enter normal operating state 300. IfPCCM 100 activates the wait signal 372 after the standby signal has beendeactivated 340, the DMA controller may enter waiting state 371. DMAcontroller 200 may then transition to normal operating state 300 afterPCCM 100 deactivates the wait signal 373.

In ready for standby mode state 320, DMA controller 200 activates thestandby signal to PCCM 325. If PCCM 100 activates the wait signal 350,DMA controller 200 may enter standby mode state 360. PCCM 100 may reduceor eliminate the power and the clock signal to circuitry in DMAcontroller 200, and the DMA controller 200 may remain in standby modestate 360 until a read or write request is to be initiated. In someembodiments of the invention, PCCM 100 may deactivate the wait signalwhen DMA controller 200 is in standby mode state 360. If DMA controller200 does not need to initiate read or write requests 361, DMA controller200 enters ready for standby mode state 320.

If DMA controller 200 receives a DMA request from microcontroller 210,communication from a target module, or a DMA channel is enabled 370, DMAcontroller 200 may exit standby mode state 360 and enter waiting state371. DMA controller 200 may enter normal operating state after PCCM 100deactivates wait signal 373. The wait signal may not be deactivateduntil power and the clock signal stabilize to a steady state level fornormal DMA controller 200 operation. Only after the wait signal has beendeactivated 370 may DMA controller 200 exit standby mode state 360 andenter normal operating state 300. In some embodiments of the invention,DMA controller 200 may not start processing related to initiating writeor read requests until PCCM 100 deactivates the wait signal. In someother embodiments, DMA controller 200 may start processing related toinitiating write or read requests before the PCCM 100 deactivates thewait signal if the necessary power and clock signal are active. DMAcontroller 200 may not communicate with target modules 225 until thewait signal is deactivated and the DMA controller 200 enters normaloperating state 300.

Returning to FIG. 2, in some embodiments of the invention, while DMAcontroller 200 transfers audio information to audio interface 235, othercomponents shown in FIG. 2 may enter power saving states if they areinactive. As described above, microcontroller unit 210 and digitalsignal processor 205 are capable of entering standby mode, andperipheral device 240 and memory storage device 245 and interconnectmodule 130 are capable of entering idle mode. In the audio informationexample above, DMA controller 200 may transfer audio information frommemory storage device 245 to audio interface 235. DSP 205 and MCU 210may be inactive and may enter standby mode. Peripheral device 240 andmemory storage device 245 may enter idle mode if conditions describedabove are met.

In some embodiments of the invention, when DMA controller 200 transfersaudio information to audio interface buffer 290, DMA controller 200,audio interface 235, interconnect module 130, memory storage device 245,and PCCM 100 may be active and receiving power and clock signals. Inthese embodiments, the remaining modules in FIG. 2 may enter powersaving states. As shown in FIG. 4, such embodiments of the invention maybe described as a first low power state 405 of the system of FIG. 2.

In some embodiments of the invention, after DMA controller 200 fillsaudio interface buffer 290, DMA controller 200 may become inactive andenter standby mode. MCU 210 and DSP 205 may remain in standby mode ifinactive, peripheral device 240 may remain in idle mode, and memorystorage device 245 and interconnect module 130 may enter idle mode.Audio interface 235 may enter idle mode because audio interface 235 isnot interacting with any modules in the device other than speaker 265.Thus, PCCM 100 may reduce or eliminate power and the clock signal tologic circuitry in audio interface 235 responsible for communicatingwith initiator modules 215, interconnect module 130, and memory storagedevice 245. However, PCCM 100 may still supply power and the clocksignal to the logic circuitry in audio interface 235 responsible fortransferring audio information to speaker 265. PCCM 100 remains activein this state and may reduce or eliminate power and the clock signal tointerconnect module 130 if no information needs to transfer. As shown inFIG. 4, such embodiments of the invention as described above may be asecond low power state 410 of the system of FIG. 2.

In some embodiments of the invention, DMA controller 200 may exitstandby mode when a DMA channel is enabled. For example in FIG. 2, DMAcontroller 200 may be in standby mode while waiting for audio interface235 to empty audio interface buffer 290. If information needs totransfer from peripheral device 240 to memory storage device 245, DMAcontroller 200 may exit standby mode, enable a DMA channel to peripheraldevice 240 and memory storage device 245, and transfer information fromperipheral device 240 to memory storage device 245. DMA controller 200may contain multiple DMA buffers (not shown in FIG. 2) for transferringinformation between different components of the device. DMA controller200 may also enter standby mode if DMA controller 200 no longerinteracts with modules other than PCCM 100.

Turning now to FIG. 4, a state diagram for the system shown in FIG. 2including a full power state 400, first low power state 405, and secondlow power state 410 is shown. In full power state 400, all or most ofthe components shown in FIG. 2 are active. For example, when a userturns on a device, such as a cellular telephone or a portable musicplayer, the device may enter full power state 400. The user may select asong to play, and after MCU/DSP has processed all or a sufficient amountof audio data, the device transitions 403 to first low power state 405as described in detail above. In first low power state 405, DMAcontroller 200 fills audio interface buffer 290 with audio informationfrom memory storage device 245. MCU 210, DSP 205, and peripheral device240 may enter power saving states if inactive.

After DMA controller 200 fills audio interface buffer 290 with audioinformation, the device transitions 415 to second low power state 410.In second low power state 410, audio interface 235 transmits the audioinformation stored in audio interface buffer 290 to speaker 265. DMAcontroller 200 may be inactive and thus may enter standby mode. PCCM 100may eliminate or reduce power and the clock signal to interconnectmodule 130. Further, memory storage device 245, peripheral device 240,and audio interface 235, as described above, may enter idle mode. Onceaudio interface buffer 290 is to be filled, audio interface 235 sends awakeup event to PCCM 100, exits idle mode, and may send a communicationto DMA controller 200. Thus, DMA controller 200 exits standby mode andthe device transitions 420 to first low power state 405. DMA controller200 fills the audio interface buffer 290 and the system returns tosecond low power state 410. In some embodiments of the invention, thedevice may transition 407 from full power state 400 to second low powerstate 410 if, for example, components in the device enter standby oridle mode as DMA controller 200 enters standby mode.

The electronic device transitions (415, 420) between first low powerstate 405 and second low power state 410 until all audio information istransferred to speaker 265 from memory storage device 245. When moredata is required, the system goes back to full power state so that theMCU/DSP can process more data. The device may exit (430, 440) from firstlow power state 405 or second low power state 410 at any time and returnto full power state 400. For example, a user may select a different songon the portable music player or activate an additional function, thusexiting the device from a low power state. Also, additional power statesmay exist in which components enter power saving states over differentsequences of state transitions.

In some embodiments of the invention, MCU/DSP audio data processing andDMA transfer are high speed operations. Transferring audio informationto the speaker may be the slowest operation in the audio interfaceexample detailed above. Thus, power may be conserved and the device mayspend a significant amount of time in second low power state 410.

Referring back to FIG. 2, in some embodiments of the invention, DMAcontroller 200 may use the same power and clock signals as interconnectmodule 130. Thus, DMA controller 200 and interconnect module 130 mayshare a power and clock connection (not shown in FIG. 2). When DMAcontroller 200 is no longer active and no initiator modules 215 ortarget modules 225 are sending information to interconnect module 130,PCCM 100 may reduce or eliminate power and clock signal to interconnectmodule 130 and DMA controller 200.

As described above, DMA controller 200 holds information in DMA buffer280 that is sent to a peripheral device such as audio interface 235. DMAcontroller 200 may also store information relating to the state of thecontroller, such as the address of information to be transferred and thedestination of the information. If DMA controller 200 contains memorystorage such as static random access memory (SRAM), the contents of DMAcontroller 200 may be lost if power is removed. Thus, DMA controller 200may contain retention registers or other memory storage devices capableof storing information when PCCM 100 removes power from DMA controller200. A retention register is described in detail in patent application“Retention Register with Normal Functionality Independent of RetentionPower Supply” by Ko, et al., Ser. No. 10/613271, filed Jul. 3, 2003.Thus, PCCM 100 may stop power to DMA controller 200 in standby modewithout losing the memory contents stored in DMA controller 200.

As shown in FIG. 2, standby mode may be implemented in an electronicdevice containing a DMA controller. Thus, power consumption by devicescontaining DMA controllers may be reduced, thereby allowing batterypowered portable electronic devices containing DMA controllers tooperate for longer periods without recharging batteries.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

1. A method, comprising: entering into a power saving mode when a memoryaccess device no longer communicates with components of an electronicdevice other than a control module; and exiting from the power savingmode when the memory access device has to communicate with components ofthe electronic device other than the control module.
 2. The method ofclaim 1, wherein the power saving mode is a standby mode.
 3. The methodof claim 1, wherein the memory access device is a direct memory access(DMA) controller.
 4. The method of claim 3, wherein the DMA controllerenters the power saving mode if all DMA channels are disabled.
 5. Themethod of claim 3, wherein the DMA controller enters the power savingmode if no communications are received and the DMA controller does notneed to perform a read request or a write request.
 6. The method ofclaim 1, comprising: limiting functionality of the memory access devicein the power saving mode; and controlling at least one clock signal tothe memory access device in the power saving mode.
 7. The method ofclaim 6, comprising: reducing power to the memory access device in thepower saving mode; and reducing power to an interconnect module when thememory access device is in the power saving mode.
 8. The method of claim6, comprising stopping power to the memory access device in the powersaving mode.
 9. The method of claim 6, comprising reducing power to amodule coupled to the memory access device, wherein the module is asource or destination of information transferred by the memory accessdevice.
 10. The method of claim 1, comprising: activating a first signalto the control module if the memory access device no longer interactswith components of the electronic device other than the control module;and allowing the memory access device communication with the controlmodule and limiting communication with other components of theelectronic device once the first signal is active.
 11. The method ofclaim 10, wherein the first signal is a standby signal.
 12. The methodof claim 10, comprising: entering into the power saving mode after thecontrol module activates a second signal; deactivating the first signalwhen an event to exit the power saving mode occurs; deactivating thesecond signal after deactivating the first signal; and exiting the powersaving mode.
 13. The method of claim 12, wherein the second signal is await signal.
 14. A method, comprising: entering a first low power statewhen a DMA controller is communicating with at least one component in adevice other than a control module; and entering a second low powerstate when the DMA controller only communicates with the control module.15. The method of claim 14, wherein entering the first low power statefurther comprises transferring information through a memory channel. 16.The method of claim 15, comprising entering the second low power statewhen the memory channel is no longer active.
 17. The method of claim 14,comprising entering the first low power state when a communication issent to the DMA controller and a memory channel is activated.
 18. Themethod of claim 14, wherein components that are not active enter a powersaving mode in the first low power state or the second low power state.19. An apparatus, comprising: a control module; a memory access deviceoperably coupled to the control module; an information source operablycoupled to the memory access device; an information destination operablycoupled to the memory access device; and wherein the memory accessdevice is capable of entering a power saving mode.
 20. The apparatus ofclaim 19, wherein the memory access device is capable of transferringinformation between the information source and the informationdestination.
 21. The apparatus of claim 19, wherein the control moduleis capable of providing power and one or more clock signals to thememory access device, information source, and information destination.22. The apparatus of claim 19, wherein the memory access device furthercomprises a plurality of retention registers.
 23. The apparatus of claim19, wherein the information destination further comprises a buffercapable of storing information.
 24. The apparatus of claim 19, whereinthe memory access device is a direct memory access (DMA) controller andthe control module is a power and clock control module (PCCM).
 25. Theapparatus of claim 19, comprising an interconnect module, wherein thememory access device couples to the information source and theinformation destination through the interconnect module.
 26. Theapparatus of claim 25, comprising: a digital signal processor (DSP)coupled to the interconnect module; a microcontroller unit (MCU) coupledto the interconnect module, wherein the information destination is anaudio interface device and the information source is a memory storagedevice; and a speaker coupled to the audio interface device, wherein thecontrol module is capable of providing power and at least one clocksignal to the interconnect module, DSP, MCU, audio interface device, andmemory storage device.
 27. The apparatus of claim 26, wherein theinterconnect module, DSP, MCU, audio interface device, and memorystorage device are each capable of entering a power saving mode.
 28. Theapparatus of claim 27, wherein the memory access device enters a powersaving mode when the interconnect module enters the power saving mode.